The present invention disclosed herein relates to a photonic device, and more particularly, to a waveguide structure and an arrayed waveguide grating structure.
The present invention has been derived from a research undertaken as a part of the information technology (IT) development business by Ministry of Information and Communication and Institute for Information Technology Advancement, Republic of Korea (Project Management No.: 2006-S-004-02, Project Title: silicon based high-speed optical interconnection IC).
Optical interconnections can be used for increasing bus speed of semiconductor devices such as a central processing unit (CPU). To exchange signals using optical interconnections, wavelength based optical signal separating technology is required. To this end, an arrayed waveguide grating (AWG) can be used as a wavelength division device. The AWG has many merits such as high-efficiency, good mass productivity, and low packaging costs. Particularly, the AWG and a semiconductor optical amplifier are necessary for realizing integrated optical devices such as a multiple wavelength laser or an integrated wavelength switch.
FIG. 1 is a plan view illustrating a typical AWG device.
Referring to FIG. 1, the AWG device includes an input star coupler 2, an arrayed waveguide structure, and an output star coupler 4 that are disposed between an input waveguide 1 and output waveguides 5. The arrayed waveguide structure includes array waveguides 3. The array waveguides 3 have different lengths and optically connect the input and output star couplers 2 and 4.
The input star coupler 2 distributes optical signals received from the input waveguide 1 to the array waveguides 3 of the arrayed waveguide structure. Here, the arrayed waveguide structure functions as a diffraction grating since the array waveguides 3 have different lengths such that optical signals output from the array waveguides 3 can be focused on different positions according to the wavelengths of the optical signals. The output waveguides 5 are connected to the different positions of the output star coupler 4 such that the optical signals can be separately transmitted to the output waveguides 5 according to their wavelengths. That is, the optical signals can be demultiplexed. On the other hand, if optical signals having proper wavelengths are input to the output waveguides 5, wavelength multiplexed optical signals are output from the input waveguide 1. That is, the AWG device can be used for wavelength multiplexing and demultiplexing. Detailed descriptions of the operational principle, design, and applications of the AWG device can be found in M. K. Smit et al, “PHASAR-Based WDM-Devices: Principles, Design and Applications,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 2, No. 2, pp. 236-250, 1996.
The performance of the AWG device can be improved by reducing AWG loss and optical signal phase errors. The AWG loss can be defined as an optical signal intensity difference between the input waveguide 1 and the output waveguides 5. The AWG loss is dependent on geometric parameters such as waveguide interval or waveguide core layer thickness. Therefore, the AWG loss can be reduced by properly adjusting geometric parameters. For example, a method of reducing a coupling loss between a star coupler and an arrayed waveguides is disclosed in W. Bogaerts et al, “Compact Wavelength-Selective Functions in Silicon-on-Insulator Photonic Wires,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 12, No. 6, pp. 1394-1401, 2006. However, the method proposed by W. Bogaerts et al has limitations in reducing phase errors of arrayed waveguides.